January 26, 2015

ADDITIONAL QUESTIONS 2014 – 5 MARK


1. Write :
(a) IUPAC name (b) Central metal ion (c) Ligand (d) Coordination number (e) Geometry of the complex [Co(en)3]Cl3
[Co(en)3]Cl3
(a) IUPAC name of [Co(en)3]Cl3                  Tris(ethylenediamine)cobalt(III) chloride                  
(b) Central metal ion                                       Cobalt(III) / Co+3 / Cobalt
(c) Ligand                                                       en / ethylenediamine / NH2 – CH2 – CH2 – NH2
(d) Coordination number                                6
(e) Geometry of the complex [Co(en)3]Cl3    Octahedral
2. What is the potential of a half-cell consisting of zinc electrode in 0.01 M ZnSO4 solution 25oC [Eo = 0.763 V].
The half-cell reaction is           Zn → Zn2+ + 2e
The Nernst equation for the oxidation half-cell reaction is
E = Eo – (0.0591/n) log [Zn2+]
The number of electrons transferred n = 2, [Zn2+] = 0.01 = 10–2 and Eo = 0.763 V.
Substituting these values in the Nernst equation we have
E = 0.763 – (0.0591/2) log 10–2
    = 0.763 – (0.0591/2) (–2)log10
    = 0.763 + 0.0591
                                                    = 0.8221 V
3. For the complex [Co(NH3)3(NO2)3] write the following :
(a) IUPAC name (b) Central metal ion (c) Ligands (d) Coordination number (e) Geometry
(a) IUPAC name                                            Triamminetrinitrocobalt(III)              
(b) Central metal ion                                       Cobalt(III) / Co+3 / Cobalt
(c) Ligands                                                     NH3 / ammine & NO2 / nitro
(d) Coordination number                                 6
(e) Geometry                                                  Octahedral
4. Show that for a first order reaction, the time required for 99.9% completion of the reaction is 10 times that required for 50% completion.

5. Write all possible isomers with the molecular formula C4H10O and name them.
Molecular formula
 Ethers
Alcohols
C4H10O
CH3CH2– O –CH2CH3
Diethyl ether /
Ethoxy ethane
CH
3– O –CH2–CH2–CH3
Methyl-n-propyl ether /
1-Methoxy propane
                CH
3
                 |
CH3– O –CH –CH3
Methyl isopropyl ether /
2-Methoxy propane
CH3–CH2–CH2–CH2–OH
n-Butyl alcohol /
1-Butanol / Propyl carbinol
          CH
3
           |
CH3–CH–CH2OH
 iso-Butyl alcohol /
2-Methyl-1-propanol /
isopropyl carbinol
                    OH
                     |
CH3–CH2–CH–CH3
sec-Butyl alcohol /
2-Butanol / Ethyl methyl carbinol
          CH
3
           |
CH3–C–OH
           |
          CH3
tert-Butyl alcohol /
2-Methyl-2-propanol /
Trimethyl carbinol
6. A zinc rod is placed in 0.095 M zinc chloride solution at 25oC. emf of this half cell is – 0.79 V. Calculate Eo Zn2+ /Zn.
Concentration of Zn2+, [Zn2+] = 0.095 M = 1 x 10 – 1 M
emf of this half cell EZn/ Zn2+  = – 0.79 V
The number of electrons transferred, n = 2
Standard potential of Zn/ Zn2+ half-cell, EoZn/ Zn2+  = ?
The half-cell reaction is: Zn2+ + 2e→ Zn
 EZn/ Zn2+   = EoZn/ Zn2+   – 0.0591/n. log 1 / [Zn2+]
 EZn/ Zn2+   = EoZn/ Zn2+   + 0.0591/2. log 0.095
      – 0.79 = EoZn/ Zn2+  + 0.02955 log (1 x 10 – 1)                  [0.095 M = 1 x 10 – 1 M
      – 0.79 = EoZn/ Zn2+    0.02955
EoZn/ Zn2+   = – 0.79 + 0.02955
EoZn/ Zn2+   = – 0.76045 V
7. How does Salicylic acid react with the following?
(a) CH3OH (b) (CH3CO)2O (c) Br2/H2O / Bromine water
(a) On heating Salicylic acid with methyl alcohol in presence of conc. H2SO4 a pleasant smelling liquid-methyl salicylate is formed.
 (b) Salicylic acid undergoes acetylation by heating with acetic anhydride to form aspirin or Acetyl salicylic acid.
 (c) Salicylic acid reacts with bromine water gives a white precipitate of tribromo phenol.
 This reaction involves bromination with decarboxylation.

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                                              1 MARK                3 MARK                 10 MARK

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